The present state of the art knows of the use of ultrasonic transducers for the generation of ultrasonic waves. Ultrasonic waves are not only used to perform mechanical work but also for the general purpose of locating objects.
A specific application of locating objects is the use of ultrasonics in burglar alarm systems. Another known application is the remote control of a valve position, specifically in the valve position of a water tap.
Ultrasonic generation is specifically known from ultrasonic transducers made from a piezo electric ceramic, for example, made from lead-zirconium-titanate. Such a polarizable piezo ceramic material has very good power capacity such that considerable ultrasonic output power can be generated using introduced electrical excitation energy at relative good conversion efficiencies. Especially good power generation can be accomplished if the ultrasonic transducer is used in the resonance mode, which means by exciting the transducer in one of its natural oscillation modes. This ultrasonic transducer is nevertheless in such a mode of a relative narrow band, that the deviations between the natural oscillation of the transducer and the frequency of the electrical excitation voltage can lead to a decrease in output power and a reduction of its conversion efficiency. In this context, it has to be taken into account that piezo electric materials are subject to a more or less pronounced, but surely not negligible, aging processes, especially with regard to its polarization, which results in changes of the natural resonance frequency.
In addition to the above mentioned material related causes, there should be taken into consideration the resonance frequency deviation in technical mass production application which are due to the individual distributions of ultrasonic transducers manufactured in mass production even when the utmost of care is taken in their manufacture.
Other causes for resonance frequency changes are contamination and/or the problem created by the transducer getting wet. In addition, the user of ultrasonic transducers has to fight the difficulties which are caused by scatter, tolerances and aging of components of the electronics required for excitation, which is due to the fact that the aging characteristics of the ceramic transducer on the one hand, and the electronic components on the other hand, can be completely different and can lead to different frequency changes.
It is therefore one of the objects of this particular invention to provide a circuit arrangement for the excitation of an ultrasonic transducer which resolves the above mentioned disadvantages, especially to make them less critical with regard to aging of the ceramic, statistical distribution in mass production of the transducers and sensitivity in regard to tolerances of the electronic components of the circuit.